In the combustion of a fuel such as coal, oil, peat, waste and the like in an industrial process plant such as a fossil-fuelled power plant, a hot process gas is generated. Such hot process gases contain, among other components, dust particles sometimes referred to as fly ash, and nitrogen oxides. Dust particles are often removed from process gas by means of a dust removal device such as an electrostatic precipitator (ESP) or a fabric filter (FF). An ESP system is disclosed in U.S. Pat. No. 4,502,872, incorporated herein in entirety by reference.
An industrial process plant may also be equipped with a selective catalytic reduction (SCR) reactor, which catalytically induces selective reduction of process gas nitrogen oxides. An SCR system is disclosed in WO 2005/114053 and U.S. Pat. No. 5,687,656 incorporated herein in entirety by reference. ESPs and SCRs are examples of gas cleaning devices useful in an industrial process plant gas cleaning system.
In such gas cleaning systems, a rectifier used to turn the gas flow as well as create an even velocity distribution may be arranged upstream with regard to process gas flow of gas cleaning devices such as ESPs, SCRs and/or FF. Rectifiers also suppress turbulence in flowing flue gas. Thereby, erosion phenomena typically occurring at the point where flue gas enters a gas cleaning device are reduced.
U.S. Pat. No. 7,063,817 describes a device for cleaning flue gas comprising a catalytic converter, with diverter walls and a rectifier placed upstream of the catalytic converter. The rectifier is placed at the point where the flue gas passage opens into the “catalyst tower”, i.e. the duct in which the catalytic converter is placed. The purpose of the diverter walls is to ensure that flue gas flow is diverted into the catalyst tower. The purpose of the rectifier is to suppress turbulence in the flowing flue gas to reduce erosion phenomena at the point where the flue gas enters the catalytic converter. The rectifier is of a lamella design composed of lamellae made from sheet-metal strips arranged in parallel to flue gas flow.
Such a rectifier requires a significant amount of material for construction and adds a significant amount of weight to the support structure. Consequently, such a rectifier is relatively expensive to construct and erection thereof in a catalyst tower is rather complicated due to the relatively great weight of the rectifier.